1. Field of the Invention
The present invention relates to a tire pressure monitoring system, and particularly to a battery-driven tire pressure monitoring system for radio transmission of a tire pressure monitor signal detected by a sensor.
2. Description of the Related Art
FIG. 5 is a block diagram which shows a basic structure of a conventional system, and FIG. 6 is a block diagram which shows an applied example of the system shown in FIG. 5. In FIG. 5, reference numeral 1 denotes a tire pressure monitoring system. Reference numerals 21, 31, 32, 33, and 41 respectively denote a pressure sensor, an analog/digital converter (A/D-C) circuit, a control circuit, a modulation circuit, and a radio frequency (RF) circuit having an amplifier. For example, a piezoresistance type semiconductor pressure sensor is used as the pressure sensor 21. Reference numerals 5 and 6 denote a driving battery power source and an antenna, respectively. The RF circuit 41 amplifies a modulation signal and performs radio transmission of a monitor signal to the main body of the vehicle via the antenna 6. The RF circuit 41 consumes the greatest amount of electric power in the monitoring system 1. In a special environment in which wire communication cannot be carried out, for example, in a rotating tire, the RF circuit 41 is important. Alternative means such as optical communication has been proposed. However, a system in which the RF circuit 41 is used, is predominant at the present.
In this type of tire for a vehicle, a valve for air pressurization is provided. A metal rim is assembled to an inner peripheral portion of the tire, for mounting to a wheel axle. The interior of the manufactured tire is maintained substantially at atmospheric pressure, and the tire is placed, for example, in a storehouse. That is, the tire is stored in a non-pressurized state. Thereafter, tires finished as products and placed in storage are transferred to a place for manufacturing various types of vehicles and mounted on axles. There are cases in which some tires are exhibited at a store for selling articles for vehicles or at a service station and tires purchased by general consumers are mounted in private cars or in vehicles used for business purposes. The tires mounted to an axle or a spare tire are each filled, via the above-described valve, with a predetermined air pressure suitable for vehicle operation.
The tire pressure monitoring system 1 is mounted on a rim or within a valve at the time of assembling the tire. Normally, when the tire pressure monitoring system 1 is mounted, simultaneously, a transmitter operation is initiated via the antenna 6. More particularly, a monitor signal is transmitted through the RF circuit 41, which unfortunately has a high consumption rate of battery power. Therefore, the life span of the battery 5 is shortened. In order to prevent power consumption by a tire in storage, prior to tire pressurization, it has been proposed to use a mechanical pressure switch Sw is, as shown in FIG. 6. The switch Sw opens the power source circuit when tire pressure is at predetermined value or less. However, during a vehicle operation, the tires are subjected to heavy vibrations while rotating. Therefore, it is difficult to provide a satisfactory mechanical switch Sw. Even if a mechanical switch is provided, a malfunction (unintended opening or closing of the switch) may be likely to occur due to the vibrations.
Further, if a pressure switch Sw is provided in the power source circuit of the battery 5, the number of parts increases, which results in increased cost for the tire pressure monitoring system 1.
Additionally, it is desirable to separately distinguish tires placed in storage or mounted in a vehicle from those used for another vehicle. Accordingly, an identification is often incorporated within the tire pressure monitoring system 1 for identifying the tire. The identifications need to be stored somewhere in the tire pressure monitoring system 1. However, when a volatile memory (RAM; see FIG. 6) for storage of identification is provided, the drawback of battery power consumption further increases, along with cost of the system, and so on.
The present invention has been devised to address the above-described conventional drawbacks, and provide a tire pressure monitoring system having advantages not provided by conventional systems.
In accordance with a first aspect of the present invention, there is provided a tire pressure monitoring system driven by a battery, comprising: a comparator which makes a comparison between a predetermined value and a detection value of any one of tire pressure and an amount related to tire pressure; and a controller which controls so as to start transmission of the detection value based on a result of the comparison by the comparator.
In accordance with a second aspect of the present invention, there is provided a tire pressure monitoring system driven by a battery, comprising: a sensor which detects any one of tire pressure and an amount related to tire pressure; a transmitter which transmits a detection value detected by the sensor; and a controller which makes a comparison between a predetermined value and the detection value detected by the sensor, and when the detection value is greater than the predetermined value, the controller controls the transmitter so as to start transmission of the detection value.
In accordance with a third aspect of the present invention, in the second aspect of the present invention, when the detection value is less than the predetermined value, the controller controls the transmitter so as not to cause transmission of the detection value.
In accordance with a fourth aspect of the present invention, in the second aspect of the present invention, after transmission of the detection value is once started, the controller controls the transmitter so as not to stop the transmission.
In accordance with a fifth aspect of the present invention, in the second aspect of the present invention, the sensor is a pressure sensor for detecting tire pressure.
In accordance with a sixth aspect of the present invention, in the second aspect of the present invention, the sensor is a temperature sensor for detecting a temperature related to tire pressure.
In accordance with a seventh aspect of the present invention, in the second aspect of the present invention, the controller includes:
a first storage device for holding the predetermined value;
a second storage device for holding the detection value;
a comparator which makes a comparison between the predetermined value held in the first storage device and the detection value held in the second storage device; and
a transmission enable flag set based on a result of the comparison by the comparator,
the controller being provided to control the transmitter based on setting of the transmission enable flag.
Further, a memory in which an identification inherent in each tire is stored is provided, and the identification is transmitted together with the detection value during the transmission.
In accordance with an eighth aspect of the present invention, there is provided a tire pressure monitoring method comprising the steps of: (a) detecting any one of tire pressure and an amount related to tire pressure; (b) comparing a detection value detected in the step (a) with a predetermined value; and (c) when the detection value is greater than the predetermined value as a result of the comparison in the step (b), starting transmission of the detection value.